1. Field of the Invention
The present invention is concerned with such image forming apparatus as electro-photographic apparatus, printers, etc. and relates to an image forming apparatus to obtain color developing images using a revolver type color developing device.
2. Description of the Related Art
For a multi-color image forming apparatus having the plural number of developing units in order to obtain color images according to electro-photographing system of color copiers, color printers, etc., the downsizing is so far demanded. In response to this demand, a revolver type color developing device is developed in recent years. In this revolver type color developing device, 3 developing units to supply yellow (Y), magenta (M) and cyan (C) toners, respectively are installed in a single rotating holder and the rotary holder further equipped with a black (BK) toner additionally is rotated to arrange the developing units in specified colors sequentially at a position opposite to the photosensitive drum and develop a latent image on the photosensitive drum.
In this revolver type color developing device, in order to obtain a highly precise developing image, it is desired to control a developing gap between the developing units and a photoreceptor precisely. In the Japanese Patent Application Publication No. 2002-287489, an image forming apparatus is disclosed. In this image forming apparatus, a photosensitive drum and a revolver type color developing device are maintained at a specified distance and a developing gap is adjusted by adjusting the position of the developing rollers by a developing roller position adjusting holder that is capable of oscillating centering around the supporting point.
However, in this conventional image forming apparatus, the positions of the developing rollers are adjusted by the rotation and movement of the developing roller position adjusting holder. Therefore, whenever the developing roller position adjusting holder is adjusted, the position of the developing roller opposing to the photosensitive drum is shifted from the line connecting the centers of the revolver type color developing device and the photosensitive drum. That is, whenever the developing roller adjusting holder is adjusted, the developing position on the photosensitive drum is shifted the optimum development by the developing roller cannot be obtained and the highly precise development of images is impeded.
Therefore, for a revolver type color developing device to achieve the downsizing of an image forming apparatus, the development of an image forming apparatus capable of easily adjusting a gap between a photosensitive drum and developing rollers without changing the developing position on the photosensitive drum and obtaining highly precise and good reproducible developer images is desired.